Solids transfer leg



July 26, 1955 D. H. STEVENSON 2,713,949

SOLIDS TRANSFER LEG Filed Feb. 24, 1951 DISENGAGIN G CHAMBER REACTOR HOPPER INVENTOR =1- l DONALD H STEVENSON United States Patent SOLIDS TRANSFER LEG Donald H. Stevenson, Cheltenham, Pa., assignor to Houdry Process Corporation, Wilmington, Del., a corporation of Delaware Application February 24, 1951, Serial N 0. 212,604

7 Claims. (Cl. 214-47) This invention relates to a moving-solids apparatus adapted to convey solid granular materials of discrete particle size in a substantially compact column from an upper zone to a lower zone, and more particularly to a moving-solids recycling apparatus in which granular solids are conveyed as a confined column from an upper zone to a lower zone while gases simultaneously flow countercurrent to the column.

Heretofore it has been the practice of conveying solids of appreciable particle size such as in the range of 14 mesh or larger, particularly as about 2m 5 millimeters, from an upper zone to a lower zone by means of a confined duct or seal leg through which the solids are passed under the influence of gravity in a substantially compact columnar form. It has also been found advantageous to introduce an inert or compatible gas at the bottom of this seal leg for the purpose of preventing or inhibiting the upward flow of vapors from the lower zone through the gravitating column to the upper zone and to maintain desired pressure differentials therebetween. It has been found, however, that there are difficulties attending this operation of the seal leg in that troublesome stoppages of particle movement through theseal leg occur when the gas velocity is excessive.

I have found that one cause for these stoppages of particle movement has been the accumulation of minute solid particles at the top of the seal leg where the narrow cross section of the seal leg intersects the wide cross section of the upper zone. This phenomenon is attributed to the fact that the upward flow of seal gas through the seal leg proceeds at a velocity which is sufiicient to lift and impel minute solid particles (formed by the attrition of the larger granular particles) upwardly through the seal leg to the upper zone where, due to the greatly increased cross section of the latter, the gas velocity is materially reduced and insulhcientto lift these particles any further whereupon they accumulate at this point.

Therefore, it is among the objects of the present invention to provide an improved seal leg of th type referred to hereinabove.

Another object is the provision of an improved seal leg of the type described which is adapted for use inja moving solids system in which both granular and minute solid particles are present and while passing therethrough a countercurrent gas flow.

A still further object is the provision of a novel seal leg, connecting an upper zone of granular solids to a lower zone, wherein an uninterrupted flow of solids is assured, when the seal leg is operated close to its maximum pressure differential. a

A further object is the attainment of the foregoing objectives while removing the minute solid particles passing through the seal leg.

The operation of the novel features of the invention and other advantages thereof Will be understood from the description which follows, read in connection with the accompanying drawings illustrating a practical embodiment thereof, as applied to a catalytic hydrocarbon conversion system.

In the drawings: Figure l is a diagrammatic elevation of a moving-bed recycling apparatus employing a preferred embodiment of the invention; and

bed recycling apparatus, as employed in the conversion or cracking of crude hydrocarbons, and wherein the numeral 10 designates a disengaging chamber the lower portion of which functions as a reservoir of granular solids. These solids are conveyed in a substantially compact gravitating columnar form through an inclined duct 11 and connecting vertical duct 12 into a reactor 13 from which they move downwardly through seal leg 13a, regenerator 14, and inclined connecting conduit 15 to a gas lift hopper 16 where they are contacted by the lift gas stream introduced through a pipe 17. The granular particles are then impelled by the lift gas stream upwardly through a vertical lift pipe 18 to the disengaging chamber 10 where they are disengaged from the lift gas stream and fall by gravity into the reservoir at the bottom of chamber 1%). The lift gas then passes through outlet conduit 24 to a cyclone separator 25 from which it is discharged to the atmosphere through pipe 26. V

A minor portion of the solids in the reservoir at the bottom of chamber 10 may be withdrawn, as through conduit 19, and moved by gravity through an elutriator 20 wherein fines are elutriated from the coarser solids, by a countercurrent flow of gas admitted through pipe 21 and discharged through pipe 22. The coarser solids, thus freed of fines, may be returned to any desired portion of the solids recycling system, as by passage through conduit 23 to the regenerator 14.

In a typical hydrocarbon cracking apparatus, the reactor 13 is conventionally provided with a hydrocarbon feed pipe 30, a vapor outlet pipe 31 and a purge gas inlet pipe 32. The connecting conduit 13a acts as a pressure seal leg between reactor 13 and regenerator 14 and is provided wih a seal gas inlet pipe 33 adapted to admit seal gas, such as steam, thereto for the purpose of prohibiting the flow of gas from the regenerator to the reactor. The regenerator 14 is conventionally provided with a regenerator gas inlet pipe 34 and a regenerator gas outlet pipe 35. The pressure seal leg, comprising ducts l1 and 12, is provided with a seal gas inlet pipe 36, for a purpose similar to that obtaining in seal leg 13a, and in a manner similar thereto.

The teachings of the present invention contemplate at least partial removal of the seal gas or vapors rising through duct 12 by means of a gas outlet pipe 37. The disposal of such removed gas and any solids entrained therein is made in any suitable fashion such as, for instance, by passing through a cyclone separator 38, which removes the solids from the gas stream and discharges the latter through vent pipe 39.

Referring now to Figure 2 it will be seen that the granular solids, passing in a gravitating substantially compact column through duct 11, are discharged into the vertical duct 12 in the course of which these solids assume the inclined upper surface 43 whose angle of inclination is substantially equal to the angle of repose of the granular solids. From this point the granular solids continue their downward movement through duct 12 to the lower moving-bed zone of reactor 13.

Overlying the inclined surface of the moving-bed at the top of the vertical duct 12 is an apertured closure member 40. communicates With a gas outlet conduit 41, the latter Patented July 26, 1955- The aperture in the closure member 40 in turn communicating with a gas outlet pipe 37 which is provided with control valve 42.

It is to be pointed out that the use of granular solids in the previously described type of moving-bed recycling apparatus is always attended with the formation of minute particles (commonly known as fines), which are formed by the attrition, or other comminution phenomena, of the considerably larger granular particles comprising the moving solids. These fines are present practically everywhere in the apparatus, and adversely affect the operation of the seal leg as in the ducts 11 and 12 of Figures 1 and 2. The gases flowing upwardly through a seal leg operated close to its maximum pressure gradient move with suflicient velocity, through the interstices of the column of granular solids, to impel or lift the minute solids or fines present therein, projecting them upwardly through the seal leg to the point where the seal leg joins the solids reservoir. At or about this point the velocity of the upwardly flowing gas stream is reduced, due to the increased cross sectional area of the solids reservoir in the disengaging chamber 10. This reduced gas velocity results in a settling and accumulation of the fines in this region. When sufiicient fines have accumulated in this region, a bridging phenomenon occurs resulting in a stoppage of movement of the granular solids into the seal leg. Such an interruption of flow of solids is undesirable in that the successful and economical operation of the cracking system depends in part on an uninterrupted solids flow.

According to the teachings of the present invention the immediately aforementioned situation is prevented by the removal of the fines passing upwardly through the seal leg. To effect the removal of these fines it is important that the upwardly flowing gas stream be disengaged and conducted away from the seal leg at a velocity which is substantially equal to, or greater than, the velocity of the gas flowing through the seal leg at the region of such disengagement. In order to insure that the velocity of the gas stream be substantially constant during its flow from the catalyst column and through conduit 41, the cross sectional area of the aperture in the closure member 40 and the cross sectional area of the conduit 41 are fixed at substantially the same value as the open area in a cross section of the moving-bed at the level of such disengagement. It has been found that the average open area in a given cross section of a moving column of granular solids is approximately 40 percent of the cross sectional area of the column. It is therefore contemplated that the cross sectional area of conduit 41 will be approximately 40 percent of the cross sectional area of the vertical duct 12. However, the conduit 41 may having a cross sectional area considerably smaller than 40 percent of that of the duct 12, so long as the velocity of the gas stream does not become sufficiently great to lift any of the granular solids from the moving column.

Another embodiment of a seal leg adapted to effect the results contemplated by the teachings of the present invention comprises two substantially vertical ducts having approximately the same cross sectional area, each duct being disposed in axial alignment and in spaced relation with respect to the other, the upper and lower ducts functioning similarly to ducts 11 and 12 respectively of Figure 2. The space between the two ducts is enclosed by a gas removal chamber having a cross sectional area which is sufliciently greater than that of either duct to provide a moving-bed of solids therein whose inclined annular upper surface (extending between the lower end of the upper duct and the side wall of the gas removal chamber) will have an area which is approximately forty percent of the cross sectional area of the vertical duct. This chamber is designed to provide an annular space above the moving-bed corresponding in purpose to the space within conduit 41 of Figure 2. The top of the gas removal chamber is provided with a gas discharge pipe functioning in a manner similar to gas outlet pipe 37 of Figure 2.

Various other embodiments of this invention may be devised without departing from the concept illustrated herein. Such variations of design include: an inclined lower duct member, and an inclined straight seal leg; all such variations employing a gas outlet duct of substantially smaller cross section than that of the seal leg.

The utilization of the present invention effects a greatly improved seal leg which is adapted to function without the stoppages of the movement of granular solids which have heretofore been caused by the accumulation of lines at the top thereof. Furthermore, the elutriating action of the gases, flowing upwardly through a seal leg employing the teachings of the present invention, reduces the amount of elutriation necessary in another region of the system. In addition, the present invention effects the added advantage of substantially decreasing the required length of the seal leg for any given pressure differential existing between upper and lower zones, disposed at either end of the seal leg, when such pressure differential lies within a critical range immediately below the maximum pressure at which, as a result of pressure drop conditions, the upward flow of gas has suflicient velocity to stop the flow of the granular solids, since the accumulation of fines at the top of the seal leg is eliminated.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim as my invention;

1. In a gas-solids contact process involving a continuous gravitational flow of granular contact material including attrited particles or fines as a compact flowing mass between an upper confined zone and a lower confined zone maintained at a substantially higher pressure than said upper zone, the method for simultaneously sealing said mass against a flow of gaseous material from said lower zone of higher pressure to said upper zone and for removing fines from said flowing mass which comprises the steps of: confining said flowing mass between said zones as a compact moving stream of uniform cross-sectional area throughout substantially its entire length; flowing at least a portion of said stream laterally at an intermediate level to form a surface thereof inclined at the angle of repose for said granular material; exposing a portion of said inclined surface having an area less than one half the cross-sectional area of said stream; introducing seal gas into the lower end of said stream at a pressure at least as great as the pressure within said lower zone, whereby seal gas is caused to flow countercurrently through the moving mass of granular material; disengaging at least a substantial major portion of the seal gas from said mass at the exposed portion of said inclined surface; collecting said disengaged seal gas together with entrained fines directly into a confined collecting zone having said exposed surface portion as its lowermost boundary and having an outlet 1 at its upper end, said collecting zone being of such crosssectional flow area, at least in the region immediately adjacent to said exposed surface, as to maintain therein a velocity of gas flow at least as great as the velocity of gas flow within the portion of said moving stream below said intermediate portion but less than the velocity required to lift granular material other than fines from said exposed surface; and withdrawing seal gas together with entrained fines at a controllable rate from said collecting zone.

2. In a system for contacting gases with granular contact material wherein said granular material continuously gravitates as a compact moving mass from an elevated source into a lower chamber maintained at a' pressure substantially higher than the pressure at said source, the

- combination of: an elongated seal pipe extending from said source to said chamber and adapted to convey said granular material as a compact moving stream of sufficient length to provide a substantial resistance to the flow of gas therebetween; means for introducing seal gas at a low level within said pipe in suflicient quantity to maintain thereat a pressure at least as great as the pressure within said chamber; means at an upper level Within said seal pipe for flowing at least a portion of said granular material laterally so as to form a surface thereof inclined at the angle of repose for said material; exposing an area of said inclined surface substantially equal to the average available gas flow area through said pipe; a gas-collecting conduit having its open lower end communicating directly withand encompassing said exposed area; and means at the upper end of said gascollecting conduit for discharging seal gas at a controllable rate from said conduit; whereby fines accompanyj;

ing said granular material are disengaged with said seal gas at said exposed surface and are conveyed by entrainment through said conduit.

3. A method as defined in claim 1 characterized in that said seal gas flows at substantially uniform velocity through said stream of contact material and within said confined collecting zone.

4. A method as defined in claim 3 wherein the crosssectional area of said confined collecting zone is less than half the cross-sectional area of said stream of contact material and substantially equal to the average available gas flow area through said stream.

5. Apparatus as defined in claim 2, wherein said exposed area of said stream is approximately 40 percent of the cross-sectional area of said stream.

6. Apparatus as defined in claim 2, wherein said seal pipe comprises an upper sloping section and a lower vertical section, said exposed surface of said compact moving stream being formed at the head of said vertical section, and said conduit forming an axial extension or" said vertical section.

7. Apparatus as defined in claim 6, wherein said exposed surface of said compact moving stream of contact material is the only unconfined portion throughout the length of said stream, so that the only available free space for collection of disengaged gases is within the opening which provides communication with said conduit.

References Cited in the file of this patent UNITED STATES PATENTS 1,285,783 Nall Nov. 26, 1918 1,825,707 Wagner Oct. 6, 1931 2,400,194 Day May 14, 1946 2,410,309 Simpson Oct. 29, 1946 2,423,813 Lechthaler July 8, 1947 2,441,724 Simpson May 18, 1948 2,461,104 Bates Feb. 8, 1949 

